Purpose: To quantify the anatomic changes caused by external beam radiotherapy in head-and-neck cancer patients in full three dimensions and to relate the local anatomic changes to the planned mean dose. Methods and Materials: A nonrigid registration method was adapted for RT image registration. The method was applied in 10 head-and-neck cancer patients, who each underwent a planning and a repeat computed tomography scan. Contoured structures (parotid, submandibular glands, and tumor) were registered in a nonrigid manner. The accuracy of the transformation was determined. The transformation results were used to summarize the anatomic changes on a local scale for the irradiated and spared glands. The volume reduction of the glands was related to the planned mean dose. Results: Transformation was accurate with a mean error of 0.6 ± 0.5 mm. The volume of all glands and the primary tumor decreased. The lateral regions of the irradiated parotid glands moved inward (average, 3 mm), and the medial regions tended to remain in the same position. The irradiated submandibular glands shrank and moved upward. The spared glands showed only a small deformation (∼1 mm in most regions). Overall, the primary tumors shrank. The volume loss of the parotid glands correlated significantly with the planned mean dose (p <0.001). Conclusion: General shrinkage and deformation of irradiated glands was seen. The spared glands showed few changes. These changes were assessed by a nonrigid registration method, which effectively described the local changes occurring in the head-and-neck region after external beam radiotherapy.

Anatomic changes, Dose-effect relation, Head and neck cancer, Nonrigid registration
dx.doi.org/10.1016/j.ijrobp.2007.10.063, hdl.handle.net/1765/29652
International Journal of Radiation: Oncology - Biology - Physics
Erasmus MC: University Medical Center Rotterdam

Vásquez Osorio, E.M, Hoogeman, M.S, Al-Mamgani, A, Teguh, D.N, Levendag, P.C, & Heijmen, B.J.M. (2008). Local Anatomic Changes in Parotid and Submandibular Glands During Radiotherapy for Oropharynx Cancer and Correlation With Dose, Studied in Detail With Nonrigid Registration. International Journal of Radiation: Oncology - Biology - Physics, 70(3), 875–882. doi:10.1016/j.ijrobp.2007.10.063